Convective Organization

Project S5 deals with the question of the organization of convective clouds. Convective clouds are a typical occurrence in the sky of warm sunny days. They exhibit a large variety in shape and size, ranging from the isolated and randomly distributed cumuli to organized cloud clusters that can span thousands of kilometers (see left and right figure).

Random distribution of cumulus clouds.

A large convective cell.

But do these different appearances of convection matter for the climate of a particular region? And if so, are some biases in state-of-the-art global climate models associated with a misrepresentation of convective organization on the meso- or sub-synoptic scales?

To answer these questions, observational signatures of convective organizations are identified and their representation is evaluated in the ICON_LEM model as well as in coarser resolution simulations using parametrized convection. The role of convective organizations is quantified for the European Summer climate and the tropical Atlantic climate. The consideration of two different climatic regimes helps us isolating the signature of convective organization and assessing the generality of the results.

Work packages 1 and 2 are based on a close collaboration between the University of Bonn, the Leibniz Institute for Tropospheric Research and the Max Planck Institute for Meteorology. Signatures of convective organizations are investigated using weather radars, geostationary satellites and ICON-LEM simulations.

In a first step, a set of organization indices has been assessed using radar and satellite data as well as a combination of the two.

Work package 3 revolves around the question if and how radiative transfer influences the formation of clouds on local and larger scales. Explorations with idealized Large-Eddy simulations revealed that radiative heating and cooling, stimulates shallow cumulus cloud dynamics, leading to the formation or destruction of cloud streets.

In work package 4, the role of sub-synoptic scale organization for the large-scale circulation is investigated. This is done by relating the dynamical properties of the convective cells to the degree of convective organization and to the large-scale circulation. Therefore Fourier and wavelet spectra of different quantities are computed to distinguish between different scales and directions of convective cells.

Work package 5 addresses the organization characteristics of shallow precipitating convection and its impact on the boundary layer turbulence. The precipitation and the associated organized motions influences the higher order moments of scalar quantities such as the moisture and potential temperature.